Pardew wildly overachieved last season, always a perilous thing for a manager to do! Now he's paid for not maintaining an impossible standard. It's worth noting, with relation to general short-termism regarding managers, that he took a while to turn West Ham round and take them back up, but the old board held their nerve.
Dowie achieved very highly at Oldham and Palace, and walked into a strange situation at the Valley (not technically manager, simply 'head coach' with a team not of his choosing) as well as having to succeed Curbishley, which was always going to be very hard. His mistake was taking the job in the first place.
Both have proven themselves fine managers in my book. But I don't get this rush to ditch Kelly anyway. He has to take the credit for the revival last season, and has hardly been allowed to bring in players. Sure he makes mistakes, but find me a manager who doesn't! It would be nice to give him a full season, something which was (understandably) denied Levein.